Particle breakage models for any particle shape in Rocky DEM
Published on: April 13, 2020
Particle breakage models help engineers in many different industries make project decisions that are possible only with the high level of accuracy gained via simulation. Improved product efficiency, better quality control, or even reduced costs are possible outcomes from such numerical results.
The unique breakage capabilities of Rocky allow to simulate with high fidelity to experimental results any particle shape. These simulations, combined with outstanding computational performance provides results in viable timeframes.
Bulk materials have one-of-a-kind shapes, aspect ratios, and material properties which are modeled in Rocky as fibers, shells, and solid particles. Depending on the type of particle, distinct breakage approaches can be applied to mimic the breakage behavior of these materials. If fibers, shells, or unique shaped solid particles are simulated, the Discrete Breakage Model is the right choice. Instant fragmentation models are useful in the comminution industry, where breakage of brittle material such as rocks or ores is easily and accurately represented.
Rocky’s breakage models also preserve the mass and volume of particles. Unlike Rocky, most DEM codes use a combination of spheres glued to each other to approximate a particle shape, but when a particle made with glued spheres is broken, volume conservation is not guaranteed.
Discrete breakage model
Fiber particles can be used to model many plant materials, such as those commonly handled in the agricultural industry. In such applications, harvesting, storage, and preparation of materials like hay, sugarcane, reeds, and bamboo can be a big problem. These materials are often transported by conveyor belts, rotors, and screws, which can compress the material and eventually break these long aspect ratio objects. Such motions can be easily accommodated in Rocky, where the particle flexibility can be configured, and shear and normal stress criteria can be used to set the limits for particle breakage.
The video below shows an example of a combine harvester, in which the breakage model for fibers can be observed.
Another form of particle representation in Rocky is shell particle shape, which is used to represent materials with a thin dimension in one main direction, such as leaves, chips, fabric, or paper. Breakage of such material is undesired in some applications, like in potato chip seasoning, as shown in the video below. On the other hand, breakage is desired in other operations in order to reduce the particle size, such as in wood chip material handling for pulp and paper manufacturing process. Lawn mowing is also a good example of an application where the shell particle model can be used combined with the breakage model to increase equipment efficiency.
Other unique shapes can be used as particles during a simulation in Rocky such as glass bottles moving on a conveyor belt, pharmaceutical tablets inside a tablet coater, or even in manufacturing bricks and roof tiles. Simulating such particle shapes is a highly complex problem, given the importance of capturing correct particle motion, which is driven by the moment of inertia and hence the particle shape. This challenge can be easily accommodated in Rocky. Also, when running Rocky simulations with the exact polyhedral shape, there is no need to input any rolling resistance parameter, as the particle shape accurately accounts for the rolling behavior.
The strength and breakage propensity of a shaped particle is quite different from that observed in a glued spheres particle, highlighting the advantage of Rocky’s particle representation for breakage analysis. With a 3D polyhedral shape, the mass and size of fragments account for stresses at the contact points, and these results aren’t predetermined by the size and number of spheres around the contact points. Furthermore, Rocky’s discrete particle breakage takes into account the particle’s collision locations and their internal stresses, capturing shape-dependent breakage and crack propagation, as seen in the video below.
Other approaches to DEM simulations in comminution processes consider particles as a single entity until the actual breakage event. In Rocky, these approaches are the Ab-T10 and Tavares models. When breakage occurs, the particle is instantaneously replaced by fragments, which are simulated as separate DEM particles and can be later re-broken.
These methods require two sets of functions: the energy strength of the particles, which determines if a particle is to be broken under applied energy; and the size distribution of the fragments being generated in the breakage process. Properly calibrated, these models can accurately predict product size distribution, throughput, forces, and power draw for the comminution devices in a reasonable amount of simulation time.
The example below shows an ore shredder, commonly used in mining applications.
Regardless of the particle shape or the application being analyzed, Rocky DEM has the appropriate breakage model for you, and all models are capable of preserving the mass and volume of the original particle. The Ab-T10 and the Tavares models allow the representation of hard materials’ brittle breakage, producing randomly shaped fragments with smaller fragments being generated closer to the impact point. Also, Rocky’s unique discrete breakage model is a high-fidelity model that considers the collision location at the particle’s surface along with its consequent internal stresses, capturing shape-dependent breakage and crack propagation.
For particle breakage prediction without the need to determine fragment size distribution, which allows for faster simulation, find more details about our Energy Spectra analysis.
Guilherme Hanauer De Lima
CAE Applications Engineer at ESSS
Guilherme is a Mechanical Engineer with a M.Sc. from the Post-Graduate Program of Mechanical and Materials Engineering (PPGEM) of Federal University of Technology, Paraná (UTFPR). He is currently working at ESSS as a CAE Applications Engineer in the Discrete Element Method (DEM) group on the Rocky DEM technical team.